1. Field of the Invention
This invention relates to systems for cooling the belt of a dry-running continuously variable transmission using the air stream through a compressor or supercharger.
2. Background & Description of the Related Art
Continuously variable transmissions, which are commonly referred to as CVTs, are used to improve fuel efficiency or horsepower utilization by allowing the drive shaft to maintain a constant angular velocity over a range of output velocities in the form of vehicle speed or angular velocity of a driven component such as a rotary compressor or supercharger. Alternatively, a CVT driven by a drive shaft of variable angular velocity may be used to precisely maintain or control the output angular velocity of the CVT output shaft. Compared with traditional gear-type transmissions having a distinct number of gear ratios, the unlimited number of gear ratios of a CVT allows the user to select a desired drive shaft angular velocity to control a desired output such as efficiency, power output, or speed. It has long been recognized in the automotive market that use of a CVT to drive a supercharger could provide significant performance enhancement. Although existing patents disclose use of a CVT with a supercharger, we are not aware of commercially available applications.
Conventional belt-driven CVTs typically comprise a variable diameter drive pulley with an input shaft, a variable diameter driven pulley with an output shaft, and an endless V-belt wrapped between the drive pulley and the driven pulley. Each pulley comprises a pair of opposing truncated cones or frustoconical sections defining an angular groove therebetween. Generally, one of the cones moves while the other remains fixed. Moving one cone in relation to the other varies the effective diameter of the pulley within which the CVT belt operates. Consequently, belt speed is a function of the effective diameter of the pulley which is, in turn, a function of the axial position of the cones relative to each other.
CVT belts typically have a profile similar to that of a conventional V-belt. In particular, they have a cross-section approximating an isosceles trapezoid; the upper edge being broader than the lower edge. The CVT belts are designed to fit between the opposing cones of the variable diameter pulleys as described above. Additionally, in order to avoid belt slippage while transferring torque from the drive pulley to the driven pulley, the cones of the driven pulley are biased axially inwardly to squeeze against the sidewalls of the CVT belt.
CVT belts have been designed to operate in wet or dry running conditions. Wet CVTs require or utilize liquid lubrication between the CVT belt and the pulley surface. As a result of this required lubrication, the orientation of wet CVTs is constrained by the need to properly distribute lubrication in the CVT housing. Dry running CVTs do not require a lubricant and therefore are not constrained to a certain orientation. In order to reduce the frictional forces in a dry running CVT, it is well known in the art that the outer inclined surface of the belt which contacts the surfaces of the pulley cones must be comprised of either thermal setting or thermal formed plastic. Using such plastics negates the need for lubrication between the belt and the pulley surfaces. However, significant frictional forces occur between the cones of the pulleys and the CVT belt. Friction results from the inward and outward movement of the CVT belt between the cones as well as from the constant compression of the cones against the CVT belt. Consequently, the friction of the CVT belt against the cones creates a significant amount of heat.
Due to the nature of the thermal setting or thermal formed plastic comprising the typical dry running CVT belts, operating temperatures of the CVT housing is limited by the operating temperature of the CVT belt. Under high temperatures, the CVT belt is susceptible to integrity failure or physical damage often times evidenced by cracking in the CVT belt or belt backing Manufacturers often suggest either removing the heat source or cooling the CVT belt from high operating temperatures.
Various methods have been employed to cool dry running CVT belts. It is known for example to attach or form vanes or ribs on the outer surface of one or more of the pulley cones to create airflow within the CVT housing that tends to assist in cooling the CVT belt and housing. See for example U.S. Pat. No. 6,176,796 to Lislegard. U.S. Published Patent Application No. 2006/0270503 by Suzuki et al., discloses a cooling system for a CVT comprising a separate fan disposed within the CVT housing at the air intake duct. The configuration and arrangement of the blades is designed to pull air through the fan, to increase speed of airflow, and to maximize the amount of airflow through the fan to cool the components of the CVT including the CVT belt.
Incorporating a fan or blower into the CVT housing or pulleys requires significant modification of the CVT or use of additional equipment and components therewith which add to the weight and cost of the CVT and increase the size of the CVT making it difficult to fit in the relatively limited space available in most engine compartments. These constraints may explain why there are patents disclosing use of a CVT to control the speed of an automobile supercharger, but such systems are not known to be commercially available. There remains a need for a system for cooling a dry running CVT which facilitates installation in the limited space available in most vehicle engine compartments and which is also suitable for industrial applications.